Method for selectively depositing a metallic film on a substrate

ABSTRACT

A method for selectively depositing a metallic film on a substrate comprising a first dielectric surface and a second metallic surface is disclosed. The method may include, exposing the substrate to a passivating agent, performing a surface treatment on the second metallic surface, and selectively depositing the metallic film on the first dielectric surface relative to the second metallic surface. Semiconductor device structures including a metallic film selectively deposited by the methods of the disclosure are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Non-Provisional of, and claims priority to, U.S. patent application Ser. No. 15/726,222 filed on Oct. 5, 2017 and entitled “A METHOD FOR SELECTIVELY DEPOSITING A METALLIC FILM ON A SUBSTRATE,” which is hereby incorporated by reference in its entirety for all purposes.

FIELD OF INVENTION

The present disclosure relates generally to methods for selectively depositing a metallic film on a substrate and particular discloses methods for selectively depositing a metallic film on a dielectric surface relative to a metal surface. The disclosure is also related to semiconductor device structures including a metallic film deposited selectively.

BACKGROUND OF THE DISCLOSURE

In some applications, it may be desirable to deposit a metallic film only on certain areas of a substrate. Typically, such discriminating results are achieved by depositing a continuous metallic film and subsequently patterning the metallic film using lithography and etch steps. Such lithography and etch processes may be time consuming and expensive, and do not offer the precision required for many applications. A possible solution is the use of selective deposition processes, whereby a metallic film is deposited only in the desired areas thereby eliminating the need for subsequent patterning steps. Selective deposition processes for semiconductor device structures may take a number of forms, including, but not limited to, selective dielectric deposition on dielectric surfaces (DoD), selective dielectric deposition on metallic surfaces (DoM), selective metal deposition on dielectric surfaces (MoD) and selective metal deposition on metallic surfaces (MoM).

Selective metal deposition on dielectric surfaces (MoD) is of interest for providing methods for selectively depositing metal films over dielectric surfaces without the need for complex patterning and etch steps. A common method for producing a substrate including selective metal over dielectric surfaces may comprise a blanket deposition of a metallic film over the entire surface of the substrate, covering both the metal surfaces and the dielectric surfaces, and subsequent forming a photolithography mask layer (or if required a double patterned mask layer) over the surface of the blanket metal film, the mask layer being disposed over the regions where the metallic film is to remain. The substrate is then exposed to a metallic etch process, such as a wet etch or a dry etch, which will remove the metallic film from the exposed regions of the substrate not covered by the photolithographic mask. Subsequent processes may remove the remaining photolithographic mask, thereby forming a substrate comprising a metallic film disposed over a dielectric surface. However, such processes for the formation of metallic films over dielectric surfaces, i.e., blanket deposition, masking and etching, are complex, time consuming, cost prohibitive and such processes only become more complex as device feature size decreases at advanced technology nodes. Accordingly, methods are desired for selectively depositing a metallic film on a dielectric surface relative to a metallic surface and particularly methods for selectively depositing tungsten films on dielectric surfaces.

SUMMARY OF THE DISCLOSURE

This summary is provided to introduce a selection of concepts in a simplified form. These concepts are described in further detail in the detailed description of example embodiments of the disclosure below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

In some embodiments, methods for selectively depositing a metallic film on a substrate comprising a first dielectric surface and a second metallic surface are provided. The method may comprise, exposing the substrate to a passivating agent, performing a surface treatment on the second metallic surface, and selectively depositing the metallic film on the first dielectric surface relative to the second metallic surface.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, the advantages of embodiments of the disclosure may be more readily ascertained from the description of certain examples of the embodiments of the disclosure when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a process flow diagram illustrating an exemplary selective deposition method according to the embodiments of the disclosure;

FIG. 2 illustrates a scanning electron microscopy (SEM) cross-sectional image of a semiconductor structure including a selective metallic film deposited according to the embodiments of the disclosure;

FIGS. 3A, 3B, 3C and 3D illustrate a method of fabricating a semiconductor device structure including a selective metallic film deposited according to the embodiments of the disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below.

The illustrations presented herein are not meant to be actual views of any particular material, structure, or device, but are merely idealized representations that are used to describe embodiments of the disclosure.

As used herein, the term “substrate” may refer to any underlying material or materials that may be used, or upon which, a device, a circuit or a film may be formed.

As used herein, the term “passivating agent” may refer to any chemical species which when applied to a surface of a material, alters at least the surface of that material in a manner which will reduce its chemical reactivity.

As used herein, the term “passivating layer” may refer to any layer, or partial layer, of material disposed over a surface which alters the surface in a manner which will reduce its chemical reactivity.

As used herein, the term “metallic surface” may refer to surfaces including a metallic component, including, but not limited to, metal surfaces, metal oxide surfaces, metal silicide surfaces, metal nitride surfaces and metal carbide surfaces.

As used herein, the term “atomic layer deposition” (ALD) may refer to a vapor deposition process in which deposition cycles, preferably a plurality of consecutive deposition cycles, are conducted in a process chamber. Typically, during each cycle the precursor is chemisorbed to a deposition surface (e.g., a substrate surface or a previously deposited underlying surface such as material from a previous ALD cycle), forming a monolayer or sub-monolayer that does not readily react with additional precursor (i.e., a self-limiting reaction). Thereafter, if necessary, a reactant (e.g., another precursor or reaction gas) may subsequently be introduced into the process chamber for use in converting the chemisorbed precursor to the desired material on the deposition surface. Typically, this reactant is capable of further reaction with the precursor. Further, purging steps may also be utilized during each cycle to remove excess precursor from the process chamber and/or remove excess reactant and/or reaction byproducts from the process chamber after conversion of the chemisorbed precursor. Further, the term “atomic layer deposition,” as used herein, is also meant to include processes designated by related terms such as, “chemical vapor atomic layer deposition”, “atomic layer epitaxy” (ALE), molecular beam epitaxy (MBE), gas source MBE, or organometallic MBE, and chemical beam epitaxy when performed with alternating pulses of precursor composition(s), reactive gas, and purge (e.g., inert carrier) gas.

As used herein, the term “film” and “thin film” may refer to any continuous or non-continuous structures and material deposited by the methods disclosed herein. For example, “film” and “thin film” could include 2D materials, nanorods, nanotubes, or nanoparticles or even partial or full molecular layers or partial or full atomic layers or clusters of atoms and/or molecules. “Film” and “thin film” may comprise material or a layer with pinholes, but still be at least partially continuous.

The embodiments of the disclosure may include methods for selectively depositing a metallic film on a substrate and particularly methods for selectively depositing a metallic film on a dielectric surface relative to a metallic surface, i.e., a metal on dielectric selective deposition process. As a non-limiting example of the embodiments of the disclosure, a tungsten film may be selectively deposited on a dielectric surface relative to a metallic surface.

The selective deposition processes described herein may be utilized to deposit a metallic film selectively on a dielectric surface without the need for additional photolithography and/or etch steps. The selective deposition processes described herein therefore simplify device fabrication processes by reducing the number of photolithographic mask stages and/or etch stages. In addition, the ability to selectively deposit a metallic film on a dielectric surface may enable improved device performance by eliminating the deposition of certain undesirable metallic films on metallic surfaces.

A possible application for selective metal on dielectric deposition processes includes the selective deposition of tungsten (W) on dielectric surfaces relative to metallic surfaces. For example, a common semiconductor device structure may comprise a metal contact structure consisting of a contact hole etched into a dielectric film, such as a silicon oxide, to reveal the underlying metal. A barrier metal, such as, for example, a titanium nitride (TiN) film may be deposited on both the side walls of the contact hole as well as on the underlying metal and a highly resistive tungsten (W) nucleation layer be deposited on the titanium nitride film. Finally, a contact plug of low resistivity tungsten (W) is utilized to complete the contact structure. However, in such a contact structure the electrical resistivity of the contact is strongly increased by the presence of the titanium nitride barrier metal and the highly resistive tungsten nucleation layer on the surface of the underlying metal contact. Utilizing a selective metal on dielectric process for tungsten deposition, the titanium nitride barrier layer may be eliminated and tungsten may be deposited directly on the sidewalls of the dielectric hole. In such a process, no titanium nitride or highly resistivity tungsten is deposited on the underlying metal and a low resistivity tungsten may be immediately deposited in the contact hole, thereby reducing the electrical contact resistance.

A selective deposition process may involve depositing a greater amount of material on a first surface relative to a second surface. For example, for a metal on dielectric selective deposition process, the selective deposition process may deposit a greater amount of a metallic film on a first dielectric surface relative to a second metallic surface. In some embodiments of the disclosure, the selectivity of the deposition process may be expressed as the ratio of material formed on the first surface relative to the amount of material formed on the first and second surfaces combined. For example, if a selective deposition process deposits 10 nm of tungsten on a first dielectric surface and 1 nm of tungsten on a second metallic surface, the selective deposition process will be considered to have 90% selectivity. In some embodiments, the selectivity of the methods disclosed herein may be above about 80%, above about 90%, above about 95%, or even about 100%. In some embodiments, the selectivity of the deposition process is at least about 80%, which may be selective enough for some particular applications. In some cases the selectivity is at least about 50%, which may be selective enough for some particular applications.

A non-limiting example embodiment of the methods of the disclosure is illustrated in FIG. 1, which illustrates method 100 for selectively depositing a metallic film on a first dielectric surface relative to a second metallic surface. The method 100 may proceed with process block 110 which may comprise providing a substrate into a first reaction chamber and heating the substrate to a process temperature.

In more detail, in some embodiments of the disclosure the, substrate may comprise a planar substrate or a patterned substrate. Patterned substrates may comprise substrates that may include semiconductor device structures formed into or onto a surface of the substrate, for example, the patterned substrates may comprise partially fabricated semiconductor device structures such as transistors and memory elements. The substrate may comprise a first dielectric surface and a second metallic surface, in other words the surface of the substrate may comprise a plurality of first dielectric surfaces and a plurality of second metallic surfaces.

In some embodiments of the disclosure, the first dielectric surface may comprise a low dielectric constant material, i.e., a low-k material, which may be defined as an insulator with a dielectric constant less than about 4.0. In some embodiments the dielectric constant of the low-k material may less than about 3.5, or less than about 3.0, or less than about 2.5, or even less than about 2.3. In some embodiments, the first dielectric surface may comprise a first silicon containing surface. For example, the first dielectric surface may comprise at least one of a silicon oxide, a silicon nitride, a silicon carbide, a silicon oxynitride, or mixtures thereof. In some embodiments of the disclosure, the first dielectric surface may comprise a porous material that contains pores which are connected to each other.

In some embodiments, the second metallic surface may comprise an elemental metal, such as, for example, copper (Cu), cobalt (Co), nickel (Ni), or tungsten (W). In some embodiments, the second metallic surface may comprise at least one of a pure metal, a metallic oxide, a metallic nitride, a metallic silicide, a metallic carbide, or mixtures thereof. In some embodiments, the second metallic surface may comprise a native oxide of metal containing material. In some embodiments, the second metallic surface may comprise a transition metal. For example, the transition metal may comprise one or more of Ti, V, Cr, Mn, Nb, Mo, Ru, Rh, Pd, Ag, Au, Hf, Ta, W, Re, Os, Ir, or Pt.

The method 100 may continue with process block 110 by loading the substrate into a suitable first reaction chamber. The first reaction chamber may be configured for performing all, or a portion, of the remaining process blocks of selective deposition method 100. In some embodiments of the disclosure, the first reaction chamber may be configured to optionally outgas the substrate (i.e., process block 120) and expose the substrate to a passivating agent (i.e., process block 130). However, in additional embodiments of the disclosure, the first reaction chamber maybe configured to perform all of the process blocks comprising selective deposition method 100.

Reactors, and their associated reaction chambers, capable of selective deposition of a metallic film on a dielectric surface can be used to perform the selective deposition method 100. Such reactors include ALD reactors, as well as CVD reactors equipped with appropriate equipment and means for providing precursors. According to some embodiments a showerhead reactor may be used. According to some embodiments a plasma reactor, such as plasma enhanced ALD reactor, may be used. Plasma may be direct or remote or in near vicinity of the substrate. According to some embodiments a thermal reactor i.e., non-plasma reactor, such as thermal ALD reactor may be used.

Examples of suitable reactors and associated reaction chambers that may be used include commercially available single substrate (or single wafer) deposition equipment such as P_(u)l_(sar)® reactors (such as the Pulsar® 2000 and the Pulsar® 3000 and Pulsar® XP ALD), and EmerALD® XP and the EmerALD® reactors, available from ASM America, Inc. of Phoenix, Ariz. and ASM Europe B.V., Almere, Netherlands. Other commercially available reactors include those from ASM Japan K.K. (Tokyo, Japan) under the tradename Eagle® XP and XP8. In some embodiments the reactor is a spatial ALD reactor, in which the substrates moves or rotates during processing.

In some embodiments a batch reactor may be used. Suitable batch reactors include, but are not limited to, Advance® 400 Series reactors commercially available from and ASM Europe B.V. (Almere, Netherlands) under the trade names A400 and A412 PLUS. In some embodiments, a vertical batch reactor is utilized in which the boat rotates during processing, such as the A412. Thus, in some embodiments, the wafers rotate during processing. In other embodiments, the batch reactor comprises a mini-batch reactor configured to accommodate 10 or fewer wafers, 8 or fewer wafers, 6 or fewer wafers, 4 or fewer wafers, or 2 wafers. In some embodiments in which a batch reactor is used, wafer-to-wafer uniformity is less than 3% (Isigma), less than 2%, less than 1% or even less than 0.5%.

The deposition processes described herein can optionally be carried out in a reactor or reaction space connected to a cluster tool. In a cluster tool, because each reaction space is dedicated to one type of process, the temperature of the reaction space in each module can be kept constant, which improves the throughput compared to a reactor in which the substrate is heated up to the process temperature before each run. Additionally, in a cluster tool it is possible to reduce the time to pump the reaction space to the desired process pressure levels between substrates.

In some embodiments of the disclosure, a stand-alone reactor can be equipped with a load-lock. In that case, it is not necessary to cool down the reaction space between each run.

Once the substrate has been loaded into the first reaction chamber, the substrate may be heated to a suitable process temperature. In some embodiments of the disclosure, process block 110 of selective deposition method 100 may comprise heating the substrate to a temperature greater than 250° C., or greater than 300° C., or greater than 350° C., or even greater than 400° C. In some embodiments of the disclosure the substrate may be heated to a temperature of approximately 250° C.

The selective deposition method 100 may continue with optional process block 120, wherein the substrate goes through an outgassing process. In some embodiments of the disclosure, the outgassing of the substrate may comprise heating the substrate to a temperature greater than 250° C. for a time period of greater than approximately 1 minute, or greater than approximately 5 minutes, or even greater than approximately 10 minutes. The outgassing of the substrate may be performed to remove unwanted species from the surface of the substrate, for example, the outgassing process may be performed to remove moisture from the substrate.

Once the substrate has undergone the optional outgassing process the selective deposition method 100 may continue with process block 130, wherein the substrate is exposed to a passivating agent. In some embodiments of the disclosure, exposing the substrate to a passivating agent may comprise exposing the substrate to an alkylhalosilane, wherein the alkylhalosilane may have the general formula X_(y)—Si—R_(4-y), wherein R is a hydrocarbon, such as, for example, an alkyl (e.g., a C1-C3 alkyl), X is a halide, such as, for example, chlorine (Cl) or fluorine (F), and y is an integer from 1 to 3, from 1 to 2, or 1. In some embodiments, exposing the substrate to a passivating agent may comprise exposing the substrate to a chemical agent having the general formula (NR^(II) ₂)_(y)—Si—R^(I) _(4-y), wherein R^(II) is a C1-C5 alkyl, R^(I) is a hydrocarbon, such as, for example, a C1-C3 alkyl, and y is an integer from 1 to 3, from 1 to 2, or 1. In some embodiments of the disclosure, exposing the substrate to a passivating agent may comprise exposing the substrate to trimethyl(dimethylamino)silane. In some embodiments, exposing the substrate to a passivating agent may comprise flowing the passivating agent into the first reaction chamber at a flow rate of approximately greater than 1 sccm, or approximately greater than 5 sccm, or approximately greater than 25 sccm, or approximately greater than 50 sccm, or approximately greater than 100 sccm, or even approximately greater than 500 sccm.

The process of exposing the substrate to a passivating agent may be performed at a substrate temperature of greater than approximately 250° C., or greater than 300° C., or great than 350° C., or even greater than 400° C. In some embodiments of the disclosure, the process of exposing the substrate to a passivating agent may be performed at a temperature of approximately 250° C. In some embodiments of the disclosure, exposing the substrate to a passivating agent may be performed for a time period of greater than 1 second, or greater than 30 seconds, or greater than 1 minute, or greater than 2 minutes, or even greater than 5 minutes. In some embodiments, exposing the substrate to a passivating agent may be performed for a time period of approximately 15 seconds. In some embodiments of the disclosure, the pressure within the first reaction chamber when exposing the substrate to the passivating agent may be less than 10 Torr, or less than 5 Torr, or even less than 2 Torr. In some embodiments of the disclosure, the pressure within the first reaction chamber when exposing the substrate to the passivating agent may be between 1 Torr and 760 Torr.

Once the substrate has been exposed to the passivating agent any remaining passivating agent may be removed from the first reaction chamber, for example, a vacuum may utilized to remove any remaining passivating agent from the first reaction chamber and/or a purge gas (e.g., nitrogen or argon) may be used to “flush” the first reaction chamber.

The selective deposition method 100 may continue with process block 140, which comprises performing a surface treatment on the second metallic surface of the substrate. For example, when the second metallic surface comprises a substantially elemental metal surface, then the surface treatment of the second metallic surface may be utilized to clean and/or reduce the second metallic surface such that a pure elemental metal is on the substrate surface. As a non-limiting example embodiment, the second metallic surface may comprise a copper surface and the surface treatment may be utilized to clean and/or reduce the copper surface to a pure elemental copper surface.

In some embodiments of the disclosure, the second metallic surface may be covered, or at least partially covered, with a passivating layer, wherein the passivating layer may reduce the reactivity of the underlying second metallic surface. For example, the second metallic surface may comprise copper and the copper may be substantially covered with a passivating layer comprising benzotriazole (BTA) or a benzotriazole derivative. For example, benzotriazole derivatives may include substituted benzotriazoles having a benzene ring substituted with hydroxy; alkoxy such as methoxy and ethoxy; amino; nitro; alkyl such as methyl, ethyl and butyl; halogen such as fluorine, chlorine, bromine and iodine. Therefore, in some embodiments of the disclosure, the second metallic surface may be at least partially covered with a passivating layer comprising benzotriazole and a surface treatment may be performed to remove the benzotriazole from the surface of the second metallic surface, for example, from the surface of a copper metal.

In some embodiments of the disclosure, removing the passivating layer from the second metallic surface may comprise exposing the passivating layer to a reactant, such as, for example, at least one of formic acid (HCOOH), acetic acid (CH₃COOH), or propanoic acid (CH₃CH₂COOH). In some embodiments, the reactant may include an alcohol. In some embodiments, the reactant may include an aldehyde. In some embodiments, the reactant may have at least one functional group selected from the group consisting of alcohol (—OH), aldehyde (—CHO), and carboxylic acid (—COOH).

Without being limited by any particular theory or mode of operation, the process for eroding and/or removing the passivating layer can include reducing one or more components of the passivating layer by using the reactant, such that at least a portion of the passivating layer may be removed from the substrate surface. In some embodiments, the passivating layer may be eroded and/or removed utilizing a reactant, including a carboxylic acid. Reaction between the passivating layer and the carboxylic acid may generate one or more volatile byproducts which may be readily transported away from the substrate surface and removed from the reaction space. For example, the carboxylic acid may reduce an oxidized copper forming part of the passivating layer such that the oxidized copper may be restored to its elemental state.

In some embodiments of the disclosure, eroding and/or removing the passivating layer may not comprise reducing one or more components of the passivating layer. For example, the reactant may interact with one or more components of the passivating layer to erode and/or remove the passivating layer without or substantially without reducing any components of the passivating layer.

Reactants containing at least one alcohol group may be selected from the group consisting of primary alcohols, secondary alcohols, tertiary alcohols, polyhydroxy alcohols, cyclic alcohols, aromatic alcohols, and other derivatives of alcohols.

In some embodiments, the primary alcohols may have an —OH group attached to a carbon atom which is bonded to another carbon atom, in particular primary alcohols according to the general formula (I):

R¹—OH  (I)

wherein R¹ is a linear or branched C₁-C₂₀ alkyl or alkenyl group, such as, for example, methyl, ethyl, propyl, butyl, pentyl, or hexyl. In non-limiting example embodiments of the disclosure, the primary alcohols may comprise methanol, ethanol, propanol, butanol, 2-methyl propanol, or 2-methyl butanol.

In some embodiments, the secondary alcohols may have an —OH group attached to a carbon atom that is bonded to two other carbon atoms. In particular, secondary alcohols may have the general formula (II):

wherein each R¹ is selected independently from the group of linear or branched C₁-C₂₀ alkyl and alkenyl groups, such as, for example, methyl, ethyl, propyl, butyl, pentyl, or hexyl. As a non-limiting example embodiment of the disclosure, the second alcohols may comprise 2-propanol, or 2-butanol.

In some embodiments, the tertiary alcohols may have an —OH group attached to a carbon atom that is bonded to three other carbon atoms. In particular, tertiary alcohols may have the general formula (III):

wherein each R¹ is selected independently from the group of linear or branched C₁-C₂₀ alkyl and alkenyl groups, such as, for example, methyl, ethyl, propyl, butyl, pentyl, or hexyl. As a non-limiting example embodiment of the disclosure, the tertiary alcohols may comprise tert-butanol.

In some embodiments, polyhydroxy alcohols, such as diols and triols, have primary, secondary and/or tertiary alcohol groups as described above. Examples of polyhydroxy alcohols include, but are not limited to, ethylene glycol and glycerol.

In some embodiments, cyclic alcohols have an —OH group attached to at least one carbon atom which is part of a ring of 1 to 10, or between 5-6 carbon atoms.

In some embodiments, aromatic alcohols have at least one —OH group attached to either a benzene ring or to a carbon atom in a side chain.

In some embodiments, reactants containing at least one aldehyde group (—CHO) are selected from the group consisting of compounds having the general formula (V), alkanedial compounds having the general formula (VI), and other derivatives of aldehydes.

Therefore, in some embodiments, the reactant may comprise an aldehyde having the general formula (V):

R³—CHO  (V)

wherein R³ is selected from the group consisting of hydrogen and linear or branched C₁-C₂₀ alkyl and alkenyl groups, such as, for example, methyl, ethyl, propyl, butyl, pentyl, or hexyl. In some embodiments, R³ is selected from the group consisting of methyl or ethyl. Examples of compounds according to formula (V) are formaldehyde, acetaldehyde and butyraldehyde.

In some embodiments, reactant are aldehydes having the general formula (VI):

OHC—R⁴—CHO  (VI)

wherein R⁴ is a linear or branched C₁-C₂₀ saturated or unsaturated hydrocarbon. Alternatively, the aldehyde groups may be directly bonded to each other (R⁴ is null).

In some embodiments, reactants containing at least one —COOH group are selected from the group consisting of compounds of the general formula (VII), polycarboxylic acids, and other derivatives of carboxylic acids.

Therefore, in some embodiments, reactants are carboxylic acids having the general formula (VII);

R⁵—COOH  (VII)

wherein R⁵ is hydrogen or linear or branched C₁-C₂₀ alkyl or alkenyl group, such as, for example, methyl, ethyl, propyl, butyl, pentyl, or hexyl. In some embodiments, R⁵ may be a linear or branched C₁-C₃ alkyl or alkenyl group. Non-limiting example embodiments of compounds according to formula (VII) may comprise formic acid, propanoic acid, or acetic acid.

In some embodiments, the reactant demonstrates desired vapor pressure such that the reactant can be volatized without heating the reactant. In some embodiments, such a reactant comprises only one carboxyl group (—COOH). In some embodiments, such a reactant may comprise dicarboxylic acid. In some embodiments, such a reactant is not a citric acid.

In some embodiments, the reactant may be heated to volatize the reactant prior to delivering the volatized reactant to the substrate surface. In some embodiments, such a reactant comprises a dicarboxylic acid, including an oxalic acid.

In some embodiments, removing the passivating layer from the second metallic surface may comprise exposing the passivating to formic acid for a time period of greater than 1 second, or greater than 25 seconds, or greater than 30 seconds, or greater than 1 minute, or greater than 2 minutes, or even greater than 5 minutes. In some embodiments of the disclosure, removing the passivating layer from the second metallic surface may comprise heating the substrate to a temperature greater than 20° C., or greater than 100° C., or greater than 150° C., or greater than 250° C., or greater than 300° C., or greater than 350° C., or even greater than 400° C. In some embodiments, removing the passivating layer from the second metallic surface may comprise heating the substrate to a temperature of approximately 250° C.

In some embodiments of the disclosure, performing a surface treatment of the second metallic surface may reduce the second metallic surface. In some embodiments the surface treatment may remove any native oxide that may be present on the second metallic surface. In some embodiments, the surface treatment may remove any hydrocarbon layer that may be present on the second metallic surface. In some embodiments, the surface treatment may provide active sites on the second metallic surface.

The surface treatment of the second metallic surface may be done in any of a variety of methods, for example, using a chemical such as formic acid or using a plasma. For example, the substrate surface may be cleaned using a hydrogen containing plasma or radicals, such as H-plasma or NH₃ plasma. In some embodiments, hydrochloric acid (HCl) treatment may be used as the surface treatment method. In some embodiments, the second metallic surface treatment process may comprise exposing the substrate to a treatment reactant, such as, for example, formic acid. Other second metallic surface treatment methods are also possible; the specific surface treatment methods to be used in any particular case can be selected based on a variety of factors, such as, the materials and the deposition conditions, including, for example, the types of materials on the substrate surface.

The selective deposition method 100 may continue with process block 150, wherein the substrate is transferred to a second reaction chamber and the substrate is heated to a desired process temperature. In some embodiments of the disclosure, the first reaction and the second reaction chamber may comprise the same reaction chamber and in such embodiments the substrate may not undergo a transfer process, i.e., the selective deposition method 100 is performed in a single reaction chamber. In alternative embodiments, the first reaction chamber and the second reaction chamber may comprise different reaction chambers and the substrate may be transferred from the first reaction chamber to the second reaction chamber. In some embodiments, the first reaction chamber and the second reaction chamber may comprise a cluster tool wherein the transfer of the substrate from the first reaction chamber to the second reaction chamber may be performed under a controlled environment without exposure to the ambient atmosphere. In some embodiments, the second reaction chamber may comprise a reaction chamber configured for a deposition process, such as, for example, an atomic layer deposition chamber or a chemical vapor deposition chamber.

Once the substrate is transferred to the second reaction chamber, the substrate may be heated to a desired process temperature. In some embodiments of the disclosure, the substrate may be heated to a desired deposition temperature in the second reaction chamber. In some embodiments, the substrate may be heated to a deposition temperature of greater than approximately 50° C., or greater than approximately 100° C., or greater than approximately 150° C., or greater than approximately 200° C., or greater than approximately 250° C., or greater than approximately 300° C., or greater than approximately 350° C., or even greater than approximately 400° C. In some embodiments of the disclosure, the substrate may be heated to a temperature of approximately 50° C.

The selective deposition method 100 may proceed with process block 160 which comprises selectively depositing a metallic film on the first dielectric surface relative to the second metallic surface. In some embodiments of the disclosure, the selective deposition process may comprise a cyclical deposition process, such as, for example, one of atomic layer deposition or cyclical chemical vapor deposition.

A non-limiting example embodiment of a cyclical deposition process may include ALD, wherein ALD is based on typically self-limiting reactions, whereby sequential and alternating pulses of reactants are used to deposit about one atomic (or molecular) monolayer of material per deposition cycle. The deposition conditions and precursors are typically selected to provide self-saturating reactions, such that an absorbed layer of one reactant leaves a surface termination that is non-reactive with the vapor phase reactants of the same reactant. The substrate is subsequently contacted with a different reactant that reacts with the previous termination to enable continued deposition. Thus, each cycle of alternating pulsed reactants typically leaves no more than about one monolayer of the desired material. However, as mentioned above, the skilled artisan will recognize that in one or more ALD cycles more than one monolayer of material may be deposited, for example, if some gas phase reactions occur despite the alternating nature of the process.

In an ALD-type process for depositing a metallic film, one deposition cycle may comprise exposing the substrate to a first reactant, removing any unreacted first reactant and reaction byproducts from the reaction space and exposing the substrate to a second reactant, followed by a second removal step. The first reactant may comprise a metal containing precursor, such as a tungsten containing precursor, and the second reactant may comprise a reducing agent precursor.

Precursors may be separated by inert gases, such as argon (Ar) or nitrogen (N₂), to prevent gas phase reactions between reactants and enable self-saturating surface reactions. In some embodiments, however, the substrate may be moved to separately contact a first vapor phase reactant and a second vapor phase reactant. Because the reactions self-saturate, strict temperature control of the substrates and precise dosage control of the precursor may not be required. However, the substrate temperature is preferably such that an incident gas species does not condense into monolayers nor decompose on the substrate surface. Surplus chemicals and reaction byproducts, if any, are removed from the substrate surface, such as by purging the reaction space or by moving the substrate, before the substrate is contacted with the next reactive chemical. Undesired gaseous molecules can be effectively expelled from the reaction space with the help of an inert purging gas. A vacuum pump may be used to assist in the purging process.

In some embodiments, cyclical deposition processes are used to selectively deposit metallic films on a substrate and the cyclical deposition process may be an ALD type process. In some embodiments, the cyclical deposition may be a hybrid ALD/CVD or cyclical CVD process. For example, in some embodiments the deposition or growth rate of the ALD process may be low compared with a CVD process. One approach to increase the growth rate may be that of operating at a higher substrate temperature than that typically employed in an ALD process, resulting in a chemical vapor deposition process, but still taking advantage of the sequential introduction or precursor, such a process may be referred to as cyclical CVD.

According to some embodiments of the disclosure, ALD processes are used to selectively deposit a metallic film on a dielectric surface of a substrate, such as an integrated circuit workpiece. In some embodiments, each ALD cycle may comprise two distinct deposition steps or phases. In a first phase of the deposition cycle (“the metal phase”), the substrate surface on which deposition is desired is contacted with a first vapor phase reactant comprising at least one metal containing vapor phase reactant which chemisorbs onto the substrate surface, forming no more than about one monolayer of reactant species on the surface of the substrate. In a second phase of the deposition cycle (“the reducing phase”), the substrate surface on which deposition is desired is contacted with a second vapor phase reactant comprising at least one reducing agent precursor which reacts with the previously chemisorbed species to selectively form a metallic film on a dielectric surface of a substrate.

In some embodiments, the metal containing precursor, also referred to here as the “metal compound” may comprise a metal. In some embodiments, the metal may comprise a transition metal. In some embodiments of the disclosure, the metal may be selected from the group of: Ti, Co, V, Cr, Mn, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir and Pt. In some embodiments the metal containing precursor may comprise at least one of Co, Ru, W, Ta, Nb, Ti, Mo, or V. In some embodiments the metal containing precursor comprises tungsten (W).

In some embodiments of the disclosure, the metal containing precursor may comprise a metal halide (F, Cl, Br, I). In some embodiments the metal containing precursor may comprise a transition metal halide. For example, as a non-limiting example embodiment, the metal containing precursor may comprise at least one of WF₆, TaF₅, NbF₅, TiF₄, MoF_(x) or VF_(x). In some embodiments of the disclosure, the metal containing precursor may comprise tungsten hexafluoride (WF₆).

In some embodiments, exposing the substrate to the at least one metal containing vapor phase reactant may comprise pulsing the metal precursor over the substrate for a time period between about 0.01 second and about 60 seconds, between about 0.05 seconds and about 10 seconds, or between about 0.1 seconds and about 5.0 seconds. In addition, during the pulsing of the metal precursor over the substrate the flow rate of the metal precursor may be less than 1000 sccm, or less than 500 sccm, or less than 250 sccm, or less than 100 sccm, or even less than 50 sccm.

Excess metal precursor and reaction byproducts (if any) may be removed from the substrate surface, e.g., by pumping with an inert gas. For example, in some embodiments of the disclosure the methods may include a purge cycle wherein the substrate surface is purged for a time period of less than approximately 2.0 seconds. Excess metal precursor and any reaction byproducts may be removed with the aid of a vacuum generated by a pumping system.

In a second phase of the deposition cycle (“the reducing phase”) the substrate is contacted with a second vapor phase reactant comprising at least one reducing agent precursor. In some embodiments of the disclosure, the at least one reducing agent containing vapor reactant may comprise at least of one of hydrogen (H₂), silane (SiH₄), disilane (Si₂H₆), trisilane (Si₃H₈), germane (GeH₄), digermane (Ge₂H₆), or diborane (B₂H₆). In some embodiments, the at least one reducing agent may comprise a plasma, such as, for example, a hydrogen plasma comprising atomic hydrogen, hydrogen ions and hydrogen radicals. In some embodiments the reducing agent precursor may comprise higher order silanes with the general empirical formula Si_(x)H_((2x+2)). In some embodiments the reducing agent precursor may comprise higher order germanes with the general empirical formula Ge_(x)H_((2x+2)).

In some embodiments, exposing the substrate to the reducing agent vapor phase reactant may comprise pulsing the reducing agent precursor (e.g., disilane) over the substrate for a time period of between about 0.01 seconds and about 60 seconds, between about 0.05 seconds and about 10 seconds, or between about 0.1 seconds and about 5.0 seconds. During the pulsing of the reducing agent precursor over the substrate the flow rate of the reducing agent precursor may be less than 1000 sccm, or less than 500 sccm, or less than 250 sccm, or less than 100 sccm, or even less than 50 sccm.

The second vapor phase reactant comprising a reducing agent reactant may react with metal-containing molecules left on the substrate. In some embodiments, the reducing agent precursor is capable of reducing the metal-containing molecules left on the substrate to form a selective elemental metal on the dielectric surfaces of the substrate. In some embodiments of the disclosure the selective elemental metal may comprise tungsten (W).

Excess second source chemical and reaction byproducts, if any, may be removed from the substrate surface, for example, by a purging gas pulse and/or vacuum generated by a pumping system. Purging gas is preferably any inert gas, such as, without limitation, argon (Ar), nitrogen (N₂), or helium (He). A phase is generally considered to immediately follow another phase if a purge (i.e., purging gas pulse) or other reactant removal step intervenes.

The deposition cycle in which the substrate is alternatively contacted with the first vapor phase reactant (i.e., the metal containing precursor) and the second vapor phase reactant (i.e., the reducing agent precursor) may be repeated two or more times until a desired thickness of a selective metallic film is deposited. It should be appreciated that in some embodiments of the disclosure, the order of the contacting of the substrate with the first phase reactant and the second vapor phase reactant may be such that the substrate is first contacted with the second vapor phase reactant followed by the first vapor phase reactant. In addition, in some embodiments, the cyclical deposition process may comprise contacting the substrate with the first vapor phase reactant (i.e., the metal containing precursor) one or more times prior to contacting the substrate with the second vapor phase reactant (i.e., the reducing agent precursor) one or more times and similarly may alternatively comprise contacting the substrate with the second vapor phase reactant one or more times prior to contacting the substrate with the first vapor phase reactant one or more times. In addition, some embodiments of the disclosure may comprise non-plasma reactants, e.g., the first and second vapor phase reactants are substantially free of ionized reactive species. In some embodiments, the first and second vapor phase reactants are substantially free of ionized reactive species, excited species or radical species. For example, both the first vapor phase reactant and the second vapor phase reactant may comprise non-plasma reactants to prevent ionization damage to the underlying substrate and the associated defects thereby created.

The cyclical deposition processes described herein, utilizing a metal containing precursor and a reducing agent precursor to form a selective metallic film on dielectric surfaces of the substrate, may be performed in an ALD or CVD deposition system with a heated substrate. For example, in some embodiments, methods may comprise heating the substrate to temperature of between approximately 50° C. and approximately 150° C., or even heating the substrate to a temperature of between approximately 50° C. and approximately 120° C. Of course, the appropriate temperature window for any given cyclical deposition process, such as, for an ALD reaction, will depend upon the surface termination and reactant species involved. Here, the temperature varies depending on the precursors being used and is generally at or below about 700° C. In some embodiments, the deposition temperature is generally at or above about 50° C. for vapor deposition processes, in some embodiments the deposition temperature is between about 50° C. and about 250° C., and in some embodiments the deposition temperature is between about 50° C. and about 200° C. In some embodiments the deposition temperature is below about 500° C., below about 400° C. or below about 300° C. In some instances the deposition temperature can be below about 200° C., below about 150° C. or below about 100° C., for example, if additional reactants or reducing agents are used in the process. In some instances the deposition temperature can be above about 20° C., above about 50° C. and above about 75° C. In some embodiments of the disclosure, the deposition temperature i.e., the temperature of the substrate during deposition is approximately 50° C.

In some embodiments the growth rate of the selective metallic film on a dielectric surface may be from about 0.005 Å/cycle to about 20 Å/cycle, from about 0.05 Å/cycle to about 10 Å/cycle from about 0.1 Å/cycle to about 10 Å/cycle, from about 1 Å/cycle to about 5 Å/cycle. In some embodiments the growth rate of the film is more than about 0.01 Å/cycle, more than about 0.05 Å/cycle, more than about 0.1 Å/cycle, more than about 0.5 Å/cycle, more than about 1 Å/cycle, more than about 1.5 Å/cycle. In some embodiments the growth rate of the film is less than about 20 Å/cycle, less than about 10 Å/cycle, less than about 5 Å/cycle, In some embodiments of the disclosure, the growth rate of the W metallic film is approximately 1.5 Å/cycle.

In additional embodiments, the selective metallic films deposited according to the embodiments of the disclosure may comprise less than about 20 atomic % oxygen, less than about 10 atomic % oxygen, less than about 5 atomic % oxygen, or even less than about 2 atomic % oxygen. In further embodiments, the selective metallic films may comprise less than about 10 atomic % hydrogen, or less than about 5 atomic % of hydrogen, or less than about 2 atomic % of hydrogen, or even less than about 1 atomic % of hydrogen. In yet further embodiments, the selective metallic films may comprise less than about 10 atomic % carbon, or less than about 5 atomic % carbon, or less than about 2 atomic % carbon, or less than about 1 atomic % of carbon, or even less than about 0.5 atomic % carbon. In the embodiments outlined herein, the atomic concentration of an element may be determined utilizing Rutherford backscattering (RB S).

In some embodiments of the disclosure, the selectively deposited metallic films may be deposited on a three-dimensional structure. In some embodiments, the step coverage of the metallic thin film may be equal to or greater than about 50%, or greater than about 80%, or greater than about 90%, or greater than about 95%, or greater than about 98%, or greater than about 99% or greater in structures having aspect ratios (height/width) of more than about 2, more than about 5, more than about 10, more than about 25, more than about 50, or even more than about 100.

In some embodiments, the selective metallic film deposited according to some of the embodiments described herein may have a thickness greater than about 20 nm, greater than about 30 nm, greater than about 40 nm, greater than about 50 nm, greater than about 60 nm, greater than about 100 nm, greater than about 250 nm, greater than about 500 nm, or greater. In some embodiments a selective metallic film deposited according to some of the embodiments described herein may have a thickness of less than about 50 nm, less than about 30 nm, less than about 20 nm, less than about 15 nm, less than about 10 nm, less than about 5 nm, less than about 3 nm, less than about 2 nm, or even less than about 1 nm.

In some embodiments of the disclosure, the selective deposition process may deposit a greater amount of a metallic film on a first dielectric surface relative to a second metallic surface. In some embodiments, the selectivity of the methods disclosed herein may be greater than approximately 80%, greater than approximately 90%, greater than approximately 95%, or even approximately 100%. In some embodiments, the selectivity of the deposition process is at least about 80%, which may be selective enough for some particular applications. In some cases the selectivity is at least about 50%, which may be selective enough for some particular applications.

As a non-limiting example embodiment of the selective deposition methods of the current disclosure, FIG. 2 illustrates a scanning electron microscopy (SEM) cross-sectional image of a semiconductor structure 200 including a selective metallic film deposited according to the embodiments of the disclosure. In more detail, FIG. 2 illustrates a semiconductor structure 200 which comprise a substrate 202, a patterned dielectric layer 204 and a metallic layer disposed in the patterned dielectric layer 206. In this non-limiting example structure the substrate 202 is a silicon substrate, the patterned dielectric layer 204 is a low-k dielectric material having a dielectric constant of 2.55, and the metallic layer disposed in the patterned dielectric layer 206 is copper. The semiconductor structure 200 also includes the selective metallic film 208, which comprises tungsten (W), which is disposed only on the surface of the low-k dielectric material and not on the surface of copper metal 206 disposed within the patterned dielectric film 204.

The selective metallic films deposited by the deposition processes disclosed herein may be utilized in a variety of contexts, such as in the formation of semiconductor device structures. One of skill in the art will recognize that the processes described herein are applicable to many contexts, including, but not limited to, device contact structures.

As a non-limiting example, FIGS. 3A-3D illustrate a method of fabricating a semiconductor device structure including a selective metallic film deposited according to the embodiments of the disclosure. It should be noted that the illustrations given in FIGS. 3A-3D only illustrate a select portion of a semiconductor device structure, i.e., the contact structure, and do not include the all the features of a completely fabricated device structure, such as, for example, the supporting substrate (e.g., a silicon substrate) and the active device structures (e.g., transistor structures).

In more detail, FIG. 3A illustrates a portion of semiconductor device structure 300 which comprises a metal contact 302, which in some embodiments may comprise a copper metal. Disposed over the metal contact 302 is an interlayer dielectric 304, which may comprise a silicon dioxide (SiO₂) or a silicon nitride (SiN). The interlayer dielectric is utilized to insulate adjacent metal lines (not shown) and reduce undesired capacitive coupling.

To interconnect the metal contact 302 with additional levels of metallization, a portion of the metal contact 302 needs to be exposed and a low resistance metal fill utilized to interconnect the different interconnection levels. In more detail, FIG. 3B illustrates semiconductor device structure 306 which comprises the metal contact 302 and a remaining portion of the interlayer dielectric 304′. The semiconductor device structure 306 also includes a contact hole 308 which may be formed by etching a portion of the interlayer dielectric 304 until the underlying metal contact is exposed, thereby exposing metallic surface 310.

The method of fabricating a semiconductor device structure according to the embodiments of the disclosure may continue with reference to FIG. 3C, wherein FIG. 3C illustrates semiconductor device structure 312 which comprises the metal contact 302, the remaining portion of the interlayer dielectric 304′, the contact hole 308 and selective metallic film 314. As illustrated in FIG. 3C, the selective metallic film 314, e.g., a tungsten (W) film, is disposed directly above the remaining interlayer dielectric 304′ and not disposed above the metal contact 310.

The fabrication of the contact structure may be completely by filling the remaining portion of the contact hole with a low resistance contact plug, as illustrated by the semiconductor device structure 316 in FIG. 3D. As illustrated in FIG. 3D, the remaining portion of the contact hole is filled with a low resistance contact plug 318, which is some embodiments may comprise a low resistance tungsten (W) contact plug. In some embodiments of the disclosure, the low resistance contact plug 318 may be deposited by the methods of the disclosure, or alternatively the low resistance contact plug 318 may be deposited by chemical vapor deposition (CVD). The semiconductor device structure 316 may be further processed to form a planar surface 320, for example, the structure may be subjected to one or more of a polishing or a chemical mechanical polishing of the upper surface of the semiconductor device structure thereby forming planar surface 320. The semiconductor device structure 316 can be further processed to add additional metal connection levels comprising one or more additional interlayer dielectric layers and metallization layers.

The embodiments of the disclosure therefore include a semiconductor device structure comprising a metallic film deposited by the methods disclosed herein. In some embodiments, the semiconductor device structure may comprise a tungsten film disposed directly over a dielectric surface. In some embodiments, the semiconductor device structure may comprise a contact structure including an interlayer dielectric and a copper contact, wherein the copper contact is not in direct contact with a barrier metal, i.e., the surface of the copper contact is free of a barrier metal, such as, for example, a titanium nitride (TiN) barrier metal. In additional embodiments of the disclosure, the contact metal, e.g., a copper contact, is not covered with a tungsten (W) nucleation layer, i.e., a high resistance tungsten (W) nucleation layer. Therefore, the embodiments of the disclosure may be utilized to fabricate a contact structure consisting of a copper contact, a selective tungsten film and a tungsten contact plug. In some embodiments, the contact structure formed by the embodiments of the disclosure may have an electrical resistivity of less than 1000 Ohm·cm², or less than 500 Ohm·cm², or less than 350 Ohm·cm², or less than 200 Ohm·cm², or even less than 100 Ohm·cm².

The example embodiments of the disclosure described above do not limit the scope of the invention, since these embodiments are merely examples of the embodiments of the invention, which is defined by the appended claims and their legal equivalents. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternative useful combination of the elements described, may become apparent to those skilled in the art from the description. Such modifications and embodiments are also intended to fall within the scope of the appended claims. 

What is claimed is:
 1. A method for selectively depositing a metallic film on a substrate comprising a first dielectric surface and a second metallic surface, the method comprising; exposing the substrate to a passivating agent; performing a surface treatment on the second metallic surface; and selectively depositing the metallic film on the first dielectric surface relative to the second metallic surface.
 2. The method of claim 1, wherein performing a surface treatment on the second metallic surface further comprises removing a passivating layer from the second metallic surface.
 3. The method of claim 1, wherein exposing the substrate to a passivating agent and performing a surface treatment on the second metallic surface are performed at a substrate temperature of greater than approximately 250° C.
 4. The method of claim 1, further comprising out-gassing the substrate prior to exposing the substrate to the passivating agent.
 5. The method of claim 4, wherein out-gassing the substrate further comprises out-gassing the substrate at temperature greater than approximately 250° C. for a time period greater than approximately 15 seconds.
 6. The method of claim 1, wherein the passivating agent comprises an alkylhalosilane.
 7. The method of claim 1, wherein the passivating agent comprises trimethyl(dimethylamino)silane.
 8. The method of claim 1, wherein exposing the substrate to a passivating agent further comprises exposing the substrate to a passivating agent for a time period of greater than 15 seconds.
 9. The method of claim 1, wherein the passivating layer comprises benzotriazole or a benzotriazole derivative.
 10. The method of claim 2, wherein removing the passivating layer from the second metallic surface comprises exposing the passivating layer to formic acid.
 11. The method of claim 10, wherein the second metallic surface comprises a copper oxide and exposing the passivating layer to formic acid reduces the copper oxide to copper.
 12. The method of claim 1, wherein exposing the substrate to a passivating agent and performing a surface treatment on the second metallic surface are performed in a first reaction chamber and selectively depositing the metallic film is performed in a second reaction chamber.
 13. The method of claim 1, wherein selectively depositing the metallic film comprises performing one or more sequential deposition cycles, each deposition cycle comprising alternating contacting the substrate with a metal containing precursor and a reducing agent precursor.
 14. The method of claim 1, wherein selectively depositing the metallic film further comprises heating the substrate to a temperature of greater than approximately 50° C.
 15. The method of claim 11, wherein the metal containing precursor comprises at least one of tungsten hexafluoride (WF₆), tantalum pentafluoride (TaF₅), niobium pentafluoride (NbF₅), titanium tetrafluoride (TiF₄), a molybdenum fluoride (MoF_(x)) or a vanadium fluoride (VF_(x)).
 16. The method of claim 11, wherein the reducing agent precursor comprises at least one of hydrogen (H₂), a hydrogen (H₂) plasma, an ammonia (NH₃) plasma, ammonia (NH₃), silane (SiH₄), disilane (Si₂H₆), trisilane (Si₃H₈), germane (GeH₄), digermane (Ge₂H₆), or diborane (B₂H₆).
 17. The method of claim 1, wherein the metallic film comprises tungsten (W).
 18. The method of claim 1, wherein the selectivity is greater than about 90%.
 19. A semiconductor device structure comprising the metallic film deposited by the method of claim
 1. 20. The semiconductor device structure of claim 19 wherein the metallic film comprises a tungsten film disposed over a dielectric surface. 